In February 1977, on a routine visit to Tehran, Sir Walter Marshall, the chief scientist at the department of Energy and deputy chairman of the UK Atomic Energy Authority, was made a seemingly impromptu “radical proposal” by the then head of the Atomic Energy Organisation, Dr Akbar Etemad for a strategic collaboration between the emergent nuclear industry of Iran and that of the UK which faced an uncertain future. Etemad’s proposal envisioned Iranian capital combining with British expertise in the form of a joint company that would be the salvation of both and mark a definitive new era in British–Iranian relations. Eighteen months of tough negotiations ended, failing to yield the desired commitment. But the encounter, largely ignored by historians sheds important new light on the politics of development in both Iran and the UK, along with the complexities of policy-making, and not least, the subtleties of the British–Iranian relationship in what would turn out to be the twilight of the Pahlavi dynasty.